Long-term measurements of SO2 dry deposition over Gansu Province, China

Potassium carbonate sulfation plates, monitored monthly for 11 years from 48 sites in 11 cities in Gansu Province, China, provide a crude estimate of cumulative SO2 dry depositions. Measured SO2 dry deposition rates were 1.6–472 mg m−2 day−1 and had seasonal variations with maxima in winter and minima mainly during summer as a result of higher winter and lower summer SO2 concentrations. The 11-year monthly average SO2 dry deposition rates are 23.2–248.97 and 11.7–175.6 mg m−2 day−1 in the eleven cities in winter and summer, respectively. A monthly average SO2 deposition velocity was also estimated from 0.06 to 9.72 cm s−2 in the 11 cities studied with a 11-year average maximum value of about 1.1–2.7 cm s−2 in April and July and a 11-year average minimum value of about 0.2–1.0 cm s−1 in January. The SO2 dry deposition velocity also exhibits an increasing with wind speed in basins of less than 500 mm annual precipitation. In contrast, due to influences of the relative humidity in valleys of more than 500 mm annual precipitation, it shows a decreasing trend with wind speed increasing.